This lesson deals with forces acting on a particle which does not move, i.e. is in equilibrium. The important concept is the resolution of forces to obtain the equations determining equilibrium. It is essential when solving such problems to start with a good diagram showing all the forces.The example introduces the idea of friction which, although simple at first sight, turns out to be quite subtle. The idea of limiting friction is introduced: this occurs when something is just on the point of slipping.
1.2 Key concepts
• Reduction of a number of forces to one resultant force by vector addition.
• Condition for equilibrium: the resultant force is zero.
• Resolution of forces in orthogonal directions to determine an unknown force.
• Frictional force; limiting friction and relation via the coefficient of friction to the normal reaction.